Electrolytic cells containing an anode, a cathode and a solid, solvent-containing electrolyte are known in the art and are usually referred to as "solid batteries". These cells offer a number of advantages over electrolytic cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features.
In solid batteries the solid electrolyte is interposed between the cathode and anode. The solid electrolyte contains either an inorganic or an organic matrix as well as a suitable inorganic salt. The inorganic matrix may be non-polymeric [e.g., .beta.-alumina, silicon dioxide, lithium iodide, etc.] or polymeric [e.g., inorganic (polyphosphazene) polymers] whereas the organic matrix is typically polymeric. Suitable organic polymeric matrices are well known in the art and are typically organic polymers obtained by polymerization of a suitable organic monomer as described, for example, in U.S. Pat. No. 4,908,283. Suitable organic constituents include, by way of example, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyepichlorohydrin, polyethylene succinate, and an acryloyl-derivatized polyalkylene oxide containing an acryloyl group of the formula CH.sub.2 .dbd.CR'C(O)O-- where R' is hydrogen or lower alkyl of from 1-6 carbon atoms. Because of the expense and difficulty in shaping inorganic non-polymeric matrices into the desired configurations, solid electrolytes containing polymeric matrices are preferred.
The solid electrolytes may also contain a solvent (plasticizer) which is typically added to the matrix in order to enhance the solubility of the inorganic salt in the solid electrolyte and thereby increase the conductivity of the electrolytic cell. Suitable solvents well known in the art for use in such solid electrolytes include, by way of example, propylene carbonate, ethylene carbonate, .gamma.-butyrolactone, tetrahydrofuran, glyme (1,2-dimethoxyethane), diglyme, triglyme, tetraglyme, dimethylsulfoxide, dioxolane, sulfolane and the like.
Successful use of lithium batteries depends on their safety during operations under normal conditions and even under abusive usage. An abusive use such as short circuiting or rapid overcharging of the battery may initiate self-heating of the battery, as opposed to merely resistive heating, leading to thermal runaway. The main processes causing self-heating of a secondary lithium cell involve the chemical reaction between cycled lithium and electrolyte. While it was previously believed that the temperature of onset of the first thermal interaction between lithium and electrolyte solvent is near 125.degree. C., it is now known that the reactions are initiated at temperatures near 100.degree. C. At temperatures greater than 100.degree. C., contributions to cell self-heating come from exothermic decomposition of the electrolyte as well as reaction between lithium and the electrolyte salt. U. von Sacken and J. R. Dahn, Abstract 54, p. 87, The Electrochem. Soc. Extended Abstracts, Vol. 90-2, Seattle, Wash., Oct. 14-19, 1990. Thermal runaway is particularly undesirable because it can lead to ignition of the electrolytic cell.
In view of the above shortcomings associated with prior art solid state electrochemical devices, there is a need for solid electrolytes that include mechanisms than can prevent thermal runaways and related problems.